The Moderna jab is the third coronavirus vaccine to be approved for use in the UK and will start to be rolled out in Wales on Wednesday 7 April.
Wales is the first UK nation to being distributing doses to its population.
Welsh Government have already said everyone in the top nine priority groups here has at least been offered their first dose of a vaccine - either Pfizer or Oxford/AstraZeneca.
It comes as a trial of the Oxford/AstraZeneca jab in children has been paused while regulators investigate a potential association between the jab and a rare form of blood clot.
The Moderna vaccine was approved for use in the UK in January this year but what do we know about it, as it begins to be rolled out here?
How safe is the Moderna jab?
Moderna, the US company behind the jab, said it had not found any serious safety concerns and the vaccine was generally well tolerated.
After receiving a first dose, side effects may include injection-site pain. After a second does, there may be fatigue, muscle or joint pain, headaches and other pain and redness at the injection site. Where these symptoms were exhibited, they were generally short-lived.
How effective is it against coronavirus?
Research suggests vaccine efficacy against the disease was 94.1% and vaccine efficacy against severe illness from Covid-19 was 100%.
More than 30,000 people in the US, from a wide range of age groups and ethnic backgrounds, took part in the trial.
In the trial, two doses were administered to participants 28 days apart. Researchers then evaluated the safety and any reaction to the vaccine.
Only 11 coronavirus cases were identified in the study's active vaccine group while 196 were observed in the placebo group - who were not given the Moderna jab.
All 30 severe cases occurred in the placebo group and none in the group which had received the vaccine.
What about new variants of the virus?
In late January, the company behind the vaccine said it was effective against both the strain first detected in south east England and the mutation which first emerged in South Africa.
While there was a reduction in neutralising antibodies produced as a result of the South African variant, it was still enough to offer protection, Moderna said.
How does it work?
Like the Pfizer jab, the Moderna one is a messenger RNA (mRNA) vaccine.
Conventional vaccines are produced using weakened forms of the virus but mRNAs use only the virus' genetic code.
Once injected, the mRNA enters the body's cells and triggers them to create antigens. These antigens are then recognised by the immune system which prepare it to fight coronavirus.
Because no actual virus is needed to create an mRNA vaccine, the rate at which the jab can be produced is often faster.
The Moderna vaccine does not need to be stored at extremely cold temperatures, like the one from Pfizer.
How many doses has the UK ordered?
The UK Government has bought 17 million doses - enough to vaccinate about 8.5 million people.
An initial 5,000 doses arrived at Glangwili Hospital in Carmarthen, as the first Moderna jabs are administered there on Wednesday April 7.
The two-dose course will be administered in Wales with a gap of between four and 12 weeks between each dose.